Composition having a base of cellulose formate capable of producing fibers of films

ABSTRACT

PCT No. PCT/CH94/00017 Sec. 371 Date Sep. 13, 1994 Sec. 102(e) Date Sep. 13, 1994 PCT Filed Jan. 26, 1994 PCT Pub. No. WO94/17136 PCT Pub. Date Aug. 4, 1994A composition having a base of cellulose formate capable of producing fibers or films, containing as solvent one or more compounds selected from the group consisting of alkylsulfoxides, lactams, acyclic amides and cyclic derivatives of urea. A process for obtaining these fibers and films. A regenerated cellulose fiber the degree of substitution of which by formate groups is less than 3%. This fiber can be used for textile applications or in order to reinforce tires.

This is a 371 of PCT/CH94/00017, filed 26 Jan. 1994.

The present invention relates to compositions for obtaining cellulosefibers or films as well as to the processes of obtaining these fibersand films, and the cellulose fibers themselves.

The production of viscose and rayon has been known for a very long time.The process for obtaining these fibers is a wet process, which hasextensive pollution characteristics.

Various processes have been described in order to try to avoid thesedrawbacks, they being summarized below.

It has been proposed to dissolve the cellulose directly in N-oxidetertiary amines, particularly the N-oxide of N-methylmorpholine, asdescribed, for instance, in U.S. Pat. No. 4,416,698, and DD 298 653.These solvents have the characteristic of easily decomposing, producingperoxides which may lead to explosions and cause the degradation of thecellulose.

It is known to prepare cellulose fibers by dissolving cellulose in amixture of N,N-dimethylacetamide (DMAC) and LiCl, as described, forinstance, in U.S. Pat. No. 4,302,252 and in EP-A-178 293, but thisprocess requires a prior activating of the cellulose and does not makeit possible to obtain fibers having mechanical properties which are asgood as those of rayon.

Japanese Patent Applications JP-A-60-199 912 and JP-A-60-209 006describe the production of fibers by using cellulose solutions inorganic solvents containing halogenated tetra-alkylammonium compounds.This process does not make it possible to exceed a concentration of 6%by weight of dissolved cellulose, which greatly limits the mechanicalproperties of the fibers obtained, in particular for industrialapplications.

Application WO-A-85/05115 describes the production of cellulose formatefibers from anisotropic solutions of cellulose formate in formic acidand phosphoric acid, which fibers can be regenerated. The process forthe obtaining of these fibers is a non-polluting process, and theregenerated cellulose fibers obtained in this manner are characterizedby very high mechanical properties; in particular, the initial modulusand the tenacity have high values. However, the fibers obtained in thisway are of a very ordered structure, which reflects the anisotropiccharacter of the starting solutions and makes them unsuitable fortextile use.

The object of the present invention is to overcome these drawbacks, orlimit them, by providing a composition capable of giving fibers orfilms, a process for the obtaining of fibers or films of regeneratedcellulose, and a regenerated cellulose fiber.

The composition in accordance with the invention, which is capable ofgiving fibers or films, and has a base of cellulose formate, ischaracterized by the following points:

a) the composition is a solution;

b) the cellulose formate concentration in the composition is equal to atleast 8% by weight;

c) the degree of substitution of the cellulose by formate groups isgreater than 20%;

d) the composition contains as solvent one or more compounds selectedfrom the group consisting of alkylsulfoxides, lactams, acyclic amides,and cyclic derivatives of urea.

These compounds may be substituted or non-substituted; the substitution,if present, is effected preferably on a nitrogen atom and thesubstituting group is preferably the methyl group.

The process of the invention for obtaining a fiber or film ofregenerated cellulose comprises the following steps:

a) the composition described above is transformed into a liquidextrudate having the shape of a fiber or film, at a temperature suchthat the solution is isotropic when at rest;

b) said liquid extrudate is coagulated;

c) the cellulose of the fiber or film thus obtained is regenerated;

d) the fiber or film which has thus been regenerated is washed anddried.

The regenerated cellulose fiber of the invention is characterized by thefollowing features:

a) the degree of substitution of the cellulose by formate groups is lessthan 3%;

b) the fiber is formed of filaments each of which has, in cross section,a morphology which is practically continuous from the periphery up tothe core;

c) the mechanical properties of the conditioned fiber are as follows:T≧10 cN/tex; M_(i) ≧500 cN/tex; A_(R) >5%; T being the tenacity, M_(i)being the initial modulus, and A_(R) being the elongation upon rupture.

The composition may contain one or more compounds selected from thegroup consisting of alkali-metal halides, alkaline-earth metal halidesand tetra-alkylammonium halides, in particular calcium chloride and/orlithium chloride.

The invention also concerns the fibers and films obtained by the processof the invention, as well as the assemblies comprising at least onefiber and/or one film in accordance with the invention.

The fibers, films and assemblies in accordance with the invention can beused, in particular, in packing, in the textile industry, or asreinforcements, for instance in order to reinforce articles of rubber orplastic materials, in particular, belts, tubes, and tires, the inventionalso concerning these articles.

The invention will be easily understood by means of the followingnon-limitative examples.

I--MEASUREMENTS AND TESTS USED 1. Measurements carried out on theinitial cellulose and on the spinning composition 1.1. Degree ofpolymerization (DP) of the cellulose

The inherent viscosity IV of the cellulose material is determined inaccordance with Swiss Standard SNV 195 598 of 1970, but at differentconcentrations which vary between 0.5 and 0.05 g/dl. The inherentviscosity is defined by the equation: ##EQU1## in which C represents theconcentration of dry cellulose material, "t" represents the time of flowof the dilute polymer solution, t₀ represents the time of flow of thepure solvent, in an Ubbelohde-type viscometer, and Ln represents thenatural logarithm, the measurements being carried out at 20° C.

The intrinsic viscosity [η] is determined by extrapolation to zeroconcentration of the inherent viscosity IV.

The average molecular weight M_(w) is given by the Mark Houwinkequation:

    [η]=KM.sub.w.sup.α

in which the constants K and α are

K=5.31×10⁻⁴ and α=0.78, these constants corresponding to the solventsystem used for the determination of the inherent viscosity.

These values are given by L. Valtasaari in Tappi 48, 627 (1965).

The degree of polymerization (DP) is defined by the formula: ##EQU2##162 being the molecular weight of the elementary unit of the cellulose.

The DP of the initial cellulose is indicated as DP_(c) in the examplesand tables which follow.

1.2. Degree of substitution (DS) of the cellulose by formate groups(degree of formylation) in the composition

The spinning composition is coagulated in water in a dispersionapparatus. After filtration, washing with water and then with acetone, apowder is obtained which is dried in air at 50° C. for at least 30minutes.

400 mg of the cellulose formate thus obtained are weighed out withprecision into a 100-ml Erlenmeyer flask; 50 ml of water and 4 ml ofnormal caustic soda solution (1N NaOH) are added. Heating is effected at100° C. with reflux for 1/2 hour under nitrogen, the cellulose beingthus regenerated from its formate. After cooling, the excess sodiumhydroxide is back-titrated with a decinormal solution of hydrochloricacid (0.1N HCl).

The total DS determined by this method gives the total percentage of thenumber of alcohol functions of the cellulose which have been esterified,that is to say DS=100% when the three alcohol functions of the unit ofthe cellulose are esterified, and DS=20% when 0.6 alcohol function isesterified.

The DS thus obtained therefore directly gives the percentage of alcoholfunctions of the cellulose which have been transformed into formategroups.

The DS of the cellulose by formate groups (degree of formylation) in thecomposition is indicated as DS_(f) in the examples and tables whichfollow.

1.3. Degree of polymerization (DP) of the cellulose in formate form inthe composition

The cellulose derivative is isolated and the cellulose of thisderivative is then regenerated by treating this derivative under refluxwith normal sodium hydroxide. The cellulose obtained is washed withwater and dried, and the DP is measured as described above in § 1.1.

The DP of the cellulose in formate form in the composition is indicatedas DP_(f) in the examples and tables which follow.

1.4. Isotropy of the solutions

A drop of the solution to be studied is placed between crossed linearpolarizer and analyzer of an optical polarizing microscope, and thenobserved at rest, that is to say in the absence of dynamic stress, atthe spinning temperature of this solution.

2. Measurements carried out on the fibers 2.1. Mechanical properties ofthe fibers

By "conditioning" there is understood the treatment of the fibers inaccordance with Federal Republic of Germany Standard DIN 53802-20/65 ofJuly 1979.

The linear density of the fibers is determined in accordance with theGerman Standard DIN 53830 of June 1965, the fibers having beenpreviously conditioned. The measurement is carried out on at least threesamples, each corresponding to a length of 50 m, by weighing this lengthof fiber. The linear density is given in tex (weight in grams of 1000meters of fiber).

The mechanical properties of the fibers (tenacity, initial modulus andelongation upon rupture) are measured by means of a traction machine ofZWICK GmbH & Co. (Federal Republic of Germany) of Type 1435 or Type1445, corresponding to German Standards DIN 51220 of October 1976, 51221of August 1976, and 51223 of December 1977, in accordance with theprocedure described in German Standard DIN 53834 of January 1979. Thefibers obtained after spinning (multifilament yarns) are imparted apreliminary protective twist for the measurement and are subjected totraction over an initial length of 400 mm. All the results are obtainedwith an average of 10 measurements.

The tenacity (T) and the initial modulus (M_(i)) are indicated in cN pertex (centinewton per tex). The elongation upon rupture (A_(R)) isindicated in percentage. The initial modulus (M_(i)) is defined as theslope of the linear part of the force-elongation curve, which is presentjust after the standard pretension of 0.5 cN/tex. T, M_(i) and A_(R) aremeasured on conditioned fibers.

2.2 Chemical properties of the regenerated fibers

The DP of the cellulose is measured in the manner indicated in § 1.1.

The determination of the DS of the regenerated fibers is effected in thefollowing manner:

About 400 mg of fiber are cut into pieces of 2-3 cm and introduced intoa 100-ml Erlenmeyer flask containing 50 ml of water. 1 ml of normalsodium hydroxide solution (1N NaOH) is added. The material is mixed atroom temperature for 15 minutes. The excess sodium hydroxide is titratedwith a decinormal solution of hydrochloric acid (0.1N HCl). The value ofDS, calculated as in § 1.2., gives the percentage of alcohol functionsof the cellulose which have been transformed into formate groups.

2.3. Morphology of the regenerated fibers

The examination is carried out with an optical polarizing microscope onelementary filaments, intact and then having undergone abrasion. Thesefilaments are observed, disposed between crossed linear polarizer andanalyzer, the axis of the filaments being parallel to the plane surfacesof the polarizer and the analyzer.

II. Production of the Fibers 1. Production of cellulose formate

The cellulose formate is prepared, for example, in accordance with theaforementioned application WO-A-85/05115 from cellulose, formic acid,and orthophosphoric acid.

In order to produce the cellulose formate, the following procedure is,by way of example, employed. Powdered cellulose (the moisture of whichis in equilibrium with the ambient humidity of the air) is introducedinto a jacketed mixer having Z-shaped arms. A mixture of orthophosphoricacid and formic acid is then added. The three components are present forinstance in the following proportions: cellulose 16%, orthophosphoricacid (99% crystalline) 46%, formic acid 38% (% by weight). Mixing iseffected for 1 hour, the temperature of the mixture being maintainedbetween 10° and 15° C. Under these conditions, for example, the DPexperiences a decrease of 30% on the average. Variation of the relativeproportion of formic acid makes it possible to vary the degree ofsubstitution.

The cellulose formate solution thus obtained is extruded from the mixerhaving Z-shaped arms by an extrusion screw in the form of liquid rods ofabout 0.5 mm in diameter which are immersed in water at roomtemperature. By coagulation and washing neutral there are obtainedcellulose formate rods which are dried with hot air at a temperature ofabout 120° C. It goes without saying that this method is mentionedmerely by way of example. The production of thin films by, for instance,extruding the solution onto the cylinders of a calendar is entirelypossible.

2. Production of the spinning compositions

The cellulose formate compositions in accordance with the invention areobtained by dissolving these rods of dry cellulose formate in thesolvents studied. The following manner of operation is, for instance,employed. The rods are placed for impregnation in the solvent at roomtemperature for a variable period of time, which may range from 1 hourto several hours. The presolution is then introduced into a jacketedmixer having Z-shaped arms. Mixing is effected for about 15 hours, thetemperature of the solution being maintained at 20°-25° C. Possibleadditives (inorganic or organic salts) may be added during the mixing.During the last hour of the mixing, a vacuum of about 8 mbar is appliedin order to degasify the solution. The solution is then extruded by anextrusion screw into a reservoir provided with a piston. The vacuum ofabout 8 mbar is maintained during the extrusion step. A faster variantconsists in maintaining the solution in the mixer at 75° C. for 2 hoursand then proceeding with the degasifying step for 1 hour at 20° C.

3. Spinning of the Composition 3.1. Spinning in accordance with thetechnique known as the technique "with non-coagulating layer of fluid"(dry jet wet)

The solution, which is at room temperature, is extruded from the storagereservoir by a piston into an extraction pump which, in its turn, pushesthe solution, in succession, through a fine cartridge filter and thespinning block up into the spinning pump. From the spinning pump, thesolution is extruded through a spinneret, preceded by a filter, thespinneret having 30, 50 or 250 orifices, each of a diameter of 65 or 50micrometers. The extrudate emerging from the spinneret is thereforeformed of 30, 50 or 250 elementary liquid veins. The liquid vein whichcomes from each orifice acquires a spinneret exit speed indicated asV_(F) in Tables 1 and 3 which follow. During the passage from thereservoir to the spinneret, the solution is progressively brought to thedesired spinning temperature (T_(F)). The spinneret is located a fewmillimeters above the coagulation bath. Before entering into thecoagulation bath, each vein which emerges from the spinneret is drawn ina non-coagulating layer of fluid, for instance, a layer of air. In thecoagulation bath, the cellulose derivative fiber is being formed. Thecoagulation bath has, for instance, a base of water within a temperature(T_(c)) range which may vary as a function of the type of fiber desired.Upon emergence from the coagulation bath, the fiber which has thus beenformed passes into a succession of washing baths having a base of waterand is then finally taken up on a drive device with a take-up speedindicated as V_(a1) in Tables 1 and 3. The temperature (T₁) of the washbaths is generally greater than that of the coagulation bath, but notnecessarily so. Upon the washing step, the fiber passes over a seconddrive device with a take-up speed indicated as V_(a2) in Tables 1 and 3.The ratio (V_(a2) /V_(F)) between the last take-up speed and the speedof emergence from the spinneret defines the total spin stretch factor,indicated as FEF in Tables 1 and 3. When V_(a2) and V_(a1) havedifferent values, there may be either a stretching of the fiber (ifV_(a2) >V_(a1)) or a relaxation of the fiber (if V_(a2) <V_(a1)) betweenthe two drive devices. The use of two drive devices is not limitativeand the process of the present invention can use a single drive deviceor more than two drive devices.

3.2. Wet spinning

The spinning conditions are identical to the preceding conditions, withthe difference that the spinneret is in contact with the coagulationbath, that is to say there is not a non-coagulating layer of fluid.

4. Regeneration of the Cellulose 4.1. Regeneration after coagulation

Upon departure from the last drive device, the wet cellulose formatefiber passes for a few seconds within a regeneration bath, generally atroom temperature, in line with the spinning step, formed, for instanceof an aqueous solution of sodium hydroxide, generally 2 to 5% by weightbut which may vary depending on the requirements, in order to regeneratethe cellulose. The regenerated fiber is then washed with water and thendried over heating rollers before being wound up.

4.2. Regeneration in the coagulation bath

One proceeds as in the preceding section, with the difference that thecoagulation bath comprises caustic soda, so that it serves both for thecoagulation and for the regeneration of the fiber. 5. Examples

A total of 29 fiber preparation tests are carried out in accordance withthe above steps 1 to 4. The conditions of these tests are given inTables 1 and 3 and the properties of the fibers obtained (multi-filamentfibers each containing 30, 50 or 250 elementary filaments) are given inTables 2 and 4. All of these tests are in accordance with the invention.

Tables 1 and 2 concern the 25 tests carried out in accordance with thedry jet wet technique, and Tables 3 and 4 concern the four tests carriedout in accordance with the wet technique.

All the percentages in Tables 1 and 3 concerning the formulation of thecompositions (solvents, additives, formate) are percentages by weight,referred to the total weight of the composition.

The abbreviations used for the solvents and for the additives are asfollows:

NMP: N-methylpyrrolidone

DMSO: dimethyl sulfoxide

DMF: N,N-dimethylformamide

TBAB: tetrabutylammonium bromide

EG: ethylene glycol

The other abbreviations as well as the units used in Tables 1 and 3, onthe one hand, and 2 and 4, on the other hand, are as follows:

DP_(c) : DP of the initial cellulose;

DP_(f) : DP of the cellulose in formate form in the composition;

DS_(f) : DS of the cellulose by formate groups (or degree offormylation) in the composition (in %);

T_(F) : Spinning temperature (in ° C.);

V_(F) : Speed of emergence from the spinneret (in m/min);

V_(a1) : First take-up speed (in m/min);

V_(a2) : Second take-up speed (in m/min);

FEF: Total spin stretch factor;

T₁ : Washing temperature (in ° C.);

T_(i) : Linear density (in tex);

T: Tenacity (in cN/tex);

A_(R) : Elongation upon rupture (in %);

M_(i) : Initial modulus (in cN/tex);

The special conditions of these tests, other than those described above,are as follows:

a) Dry jet wet technique (Table 1):

the spinneret comprises 250 holes of a diameter of 65 μm for tests 1 to11 on the one hand and 13 to 23 on the other hand, 250 holes of adiameter of 50 μm for test 12, 50 holes of a diameter of 65μm for test24, and 30 holes of a diameter of 65 μm for test 25;

the non-coagulating layer of air has a thickness of between 5 and 6 mm;

the coagulation bath consists of water containing about 12% of the totalof solvent and additive, in the same relative proportions as for thespinning compositions except in the case of test 10, where the watercontains 10% NMP and 8.6% CaCl₂, and in the case of test 14 in which thewater contains 24% NMP and less than 0.5% CaCl₂ ;

the regeneration is effected by means of an aqueous solution of sodiumhydroxide containing 5% NaOH in tests 1 to 23, and 2% NaOH in tests 24and 25;

the fibers are dried, after regeneration and washing, at a temperatureranging from 105° to 120° C.;

the fibers thus obtained are therefore multifilament yarns formed of 250filaments in tests 1 to 23, of 50 filaments in test 24, and of 30filaments in test 25;

b) Wet technique (Table 3):

the spinneret comprises 250 holes of a diameter of 50 μm for test 1, 50holes of a diameter of 65 μm for test 2, and 50 holes of a diameter of50 μm for tests 3 and 4;

the coagulation bath is formed of water containing about 12% solvent inthe same relative proportions as for the spinning compositions if amixture of solvents is concerned (test 2);

the regeneration is effected by means of an aqueous sodium hydroxidesolution containing 5% NaOH in test 1 and 2% NaOH in tests 2 to 3; inthe case of test 4, 2% NaOH was used directly in the coagulation bath;

the fibers are dried, after regeneration and washing, at a temperatureof 120° C. in test 1, 105° C. in test 2, and 90° C. in tests 3 and 4;

the fibers thus obtained are therefore spun fibers formed of 250filaments in test 1, and 50 filaments in tests 2 to 4.

In all the examples considered, the fibers obtained (Tables 2 and 4)have a degree of substitution by formate groups which is less than 2%and a degree of polymerization which is substantially equivalent to thedegree of polymerization determined for the spinning compositions(DP_(f)), this signifying that the process does not result in anysubstantial decrease in the DP of the cellulose.

                                      TABLE 1                                     __________________________________________________________________________    CONDITIONS OF THE TESTS: DRY JET WET TECHNIQUE                                       Spinning Compositions                                                                              Cellulose                                                                          Spinning                                     Test       DS.sub.f                                                                         Solvant Additive,                                                                           formate                                                                            T.sub.F                                                                          V.sub.F                                                                            T.sub.C                                                                           V.sub.a1                                                                           V.sub.a2                                                                            FEF                                                                              T.sub.1            No. DP.sub.c                                                                         DP.sub.F                                                                          (%)                                                                              Type/%  type/%                                                                              (%)  (°C.)                                                                     (m/min)                                                                            (°C.)                                                                      (m/min)                                                                            (m/min)                                                                             total                                                                            (°C.)       __________________________________________________________________________     1  1400                                                                             920 42 NMP/70  CaCl.sub.2 /8                                                                       22   69 41   4   124  135   3.3                                                                              13                  2  1400                                                                             930 38 NMP/76  CaCl.sub.2 /7                                                                       17   73 48   6   128  130   2.7                                                                              50                  3  1400                                                                             930 38 NMP/76  CaCl.sub.2 /7                                                                       17   53 52   48  128  130   2.5                                                                              50                  4  1400                                                                             910 36 NMP/78  CaCl.sub.2 /8                                                                       14   51 41   8    82   82   2.0                                                                              11                  5  1200                                                                             870 35 NMP/79  CaCl.sub.2 /9                                                                       12   60 59   8   130  130   2.2                                                                              50                  6   500                                                                             480 42 NMP/63  CaCl.sub.2 /7                                                                       30   81 19   2    82   82   4.3                                                                              11                  7  1400                                                                             850 36 NMP/65  CaCl.sub.2 /10                                                                      25   99 17   3    82   82   4.8                                                                              50                  8  1400                                                                             960 40 NMP/69  CaCl.sub.2 /11                                                                      20   115                                                                              55   4   204  204   3.7                                                                              10                  9  1400                                                                             610 37 NMP/66  CaCl.sub.2 /12                                                                      22   84 35   3   200  200   5.7                                                                              10                 10  1400                                                                             610 37 NMP/66  CaCl.sub.2 /12                                                                      22   85 40   -4  200  200   5.0                                                                              10                 11  1400                                                                             690 35 NMP/65  CaCl.sub.2 /12                                                                      23   94 28   2   160  160   5.7                                                                              10                 12  1200                                                                             820 35 NMP/68  CaCl.sub.2 /11                                                                      21   91 53   2   159  159   3.0                                                                              50                 13  1200                                                                             850 37 NMP/67  LiCl/8                                                                              25   104                                                                              28   2   120  120   4.3                                                                              50                 14  1200                                                                             810 40 NMP/68  CaCl.sub.2 /6.6                                                                     23   103                                                                              36   0   180  180   5.0                                                                              50                                       LiCl/2.4                                                15  1200                                                                             840 37 NMP/64  --    24   49 26   0   140  140   5.4                                                                              50                               DMSO/12                                                         16  1200                                                                             780 41 NMP/73  --    27   44 16   0    80   80   5.0                                                                              50                 17  1400                                                                             1110                                                                              44 DMSO/76 --    24   58 28   14  140  140   5.0                                                                              50                 18  1400                                                                             1110                                                                              42 NMP/38  --    24   58 34   0   150  150   4.4                                                                              50                               DMSO/38                                                         19  1400                                                                             1100                                                                              42 NMP/45.2                                                                              --      9.6                                                                              74 123  0   160  160   1.3                                                                              50                               DMSO/45.2                                                       20  1400                                                                             1080                                                                              42 DMF/68.4                                                                              LiCl/7.6                                                                            24   95 37   0   160  170   4.6                                                                              10                 21  1400                                                                             1150                                                                              42 DMF/80.8                                                                              LiCl/9.6                                                                              9.6                                                                              43 111  1   100  100   0.9                                                                              10                 22  1400                                                                             970 31 NMP/80.8                                                                              LiCl/9.6                                                                              9.6                                                                              64 119  2   190  190   1.6                                                                              10                 23  1400                                                                             1070                                                                              43 DMSO/66 TBAB/10                                                                             24   57 31   5   201  201   6.5                                                                              50                 24  1200                                                                             850 36 NMP/83.4                                                                              CaCl.sub.2 /2                                                                         8.6                                                                               0 40   23   40   40   1.0                                                                              10                                       H.sub.2 O/6                                             25   550                                                                             500 40 NMP/75.2                                                                              CaCl.sub.2 /4                                                                         14.8                                                                             49 36   21   40   40   1.1                                                                              20                                       EG/6                                                    __________________________________________________________________________

                  TABLE 2                                                         ______________________________________                                        CHARACTERISTICS OF THE FIBERS OBTAINED                                        UNDER THE CONDITIONS OF TABLE 1                                                         T.sub.i                                                                              T           A.sub.R                                                                            M.sub.i                                     Test No.  (tex)  (cN/tex)    (%)  (cN/tex)                                    ______________________________________                                         1        48.0   36.5        5.6  1550                                         2        45.7   37.5        7.2  1475                                         3        52.2   28.4        6.9  1386                                         4        51.1   30.6        8.7  1428                                         5        38.8   23.6        5.8  1304                                         6        52.7   37.5        9.5  1229                                         7        40.9   50.1        8.2  1644                                         8        39.7   44.1        7.9  1568                                         9        28.3   52.4        6.3  1937                                        10        32.7   51.0        6.1  1980                                        11        31.1   54.2        7.6  1921                                        12        32.5   48.6        7.3  1818                                        13        43.7   52.0        7.4  1939                                        14        42.4   42.3        6.2  1771                                        15        34.1   44.4        8.2  1678                                        16        42.0   44.0        8.7  1603                                        17        35.1   42.5        7.3  1654                                        18        40.8   38.9        7.0  1556                                        19        53.9   21.2        6.2  1078                                        20        40.5   45.5        7.8  1580                                        21        78.0   20.8        9.4  1007                                        22        46.0   21.4        5.3  1043                                        23        27.3   46.4        7.0  1697                                        24        13.5   18.9        11.9  979                                        25        11.9   17.6        12.3  989                                        ______________________________________                                    

                                      TABLE 3                                     __________________________________________________________________________    CONDITIONS OF THE TESTS (WET TECHNIQUE)                                              Spinning Compositions                                                                              Cellulose                                                                          Spinning                                     Test       DS.sub.f                                                                         Solvant Additive,                                                                           formate                                                                            T.sub.F                                                                           V.sub.F                                                                            T.sub.C                                                                          V.sub.a1                                                                           V.sub.a2                                                                            FEF                                                                              T.sub.1            No. DP.sub.c                                                                         DP.sub.F                                                                          (%)                                                                              Type/%  type/%                                                                              (%)  (°C.)                                                                      (m/min)                                                                            (°C.)                                                                     (m/min)                                                                            (m/min)                                                                             total                                                                            (°C.)       __________________________________________________________________________    1    550                                                                             420 41.5                                                                             NMP/83.7                                                                              --    16.3 30  50   30 60   70    1.4                                                                              30                 2   1400                                                                             960 38.3                                                                             NMP/81.5                                                                              --    8.5  20  25   20 30   30    1.2                                                                              20                               DMSO/10                                                         3    550                                                                             480 39.0                                                                             DMSO/91 --    9.0  30  75   30 40   60    0.8                                                                              50                 4    550                                                                             480 39.0                                                                             DMSO/91 --    9.0  30  53   30 48   48    0.9                                                                              50                 __________________________________________________________________________

                  TABLE 4                                                         ______________________________________                                        CHARACTERISTICS OF THE FIBERS OBTAINED                                        UNDER THE CONDITIONS OF TABLE 3                                                         T.sub.i                                                                              T           A.sub.R                                                                            M.sub.i                                     Test No.  (tex)  (cN/tex)    (%)  (cN/tex)                                    ______________________________________                                        1         55.7   14.3         8.7 888                                         2         11.2   15.4        12.2 843                                         3         10.3   15.9         6.7 937                                         4          8.7   11.4        14.3 636                                         ______________________________________                                    

Upon the production of the cellulose formate, the use of 99%orthophosphoric acid and formic acid makes it possible to obtain a highdegree of substitution of more than 20% and a homogeneous distributionof these formate groups, both in the amorphous zones and in thecrystalline zones of the cellulose.

Other processes for the obtaining of the cellulose formate are possible,these processes being preferably carried out in solution in order toobtain this homogeneous distribution of the formate groups.

The spinning composition produced consists of a solution in all cases.The additives are dissolved in this solution, forming at times complexeswith the solvent.

These solutions, when at rest, exhibit no anisotropy at the spinningtemperatures; they are therefore isotropic at these temperatures. It mayhappen that some of these solutions are anisotropic at rest withinparticular temperature ranges, but the spinning temperatures are alwaystaken from outside of these ranges.

Upon the spinning by the technique of non-coagulating layer of fluid(dry jet wet) and in the case of a single pure solvent without additive(tests 16 and 17 of Table 1), it is preferable to have cellulose formateconcentrations of more than 20% by weight since such a spinning becomesdifficult with lower concentrations. The addition of the salts, inparticular the calcium chloride or the lithium chloride, permits thespinning by dry jet wet within a wide range of formate concentrations,above 8% by weight, whether this concentration is less than or greaterthan 20%. Such an addition is therefore preferred for the dry jet wettechnique, except in the case that the solvent is a mixture of puresolvents without additive (for instance NMP+DMSO in examples 15, 18 and19 of Table 1).

The fibers obtained in accordance with the invention have a morphologywhich is very different from the morphology in layers which is obtainedwith anisotropic spinning compositions, such as that described, forinstance, in Application WO-A-85/05115 referred to above. In fact, theelementary filaments of the fibers in accordance with the inventionhave, in cross section, a morphology which is practically continuousfrom the periphery up to the core.

It is understood by these terms that these elementary filaments do notcontain a succession of numerous layers embedded one within the othersurrounding the axis of these filaments. Upon rubbing between them, thefibers in accordance with the invention therefore have a far betterresistance to fibrillation than the fibers described in theaforementioned application WO-A-85/05115.

The process in accordance with the invention has the followingadvantages:

It does not result in pollution under the conditions of use, as comparedwith the viscose or rayon processes;

It presents no danger, for example no risk of explosion need be fearedsince there is no formation of peroxide;

It is economical, since it permits high spinning speeds and highconcentrations of cellulose formate;

It can be used within a very wide range of concentrations of celluloseformate and it can therefore be used to produce fibers the lineardensity and mechanical properties of which vary to a great extent;

The recycling of the liquids used is easy.

The fiber in accordance with the invention has the following advantages:

The mechanical properties (tenacity, initial modulus, elongation uponrupture) and the linear density can be modulated within wide limits bycontrolling the degree of polymerization of the cellulose and theconcentration of cellulose formate in the spinning composition. In thisway, for instance, one can obtain a technical fiber, that is to say afiber having a high tenacity and a high initial modulus, the tenacityand initial modulus values of which are at least as good as those ofrayon.

The preferred characteristics of the composition of the invention are asfollows:

The content of water and/or of alcohol or alcohols is less than 10% ofthe weight of the solvent or solvents;

The DS of the cellulose by formate groups (DS_(f)) is greater than 30%.

In the event that the composition in accordance with the invention isintended for the manufacture of an industrial fiber, it preferably hasat least one of the following characteristics:

The DP of the cellulose in the cellulose formate is at least equal to500;

The composition contains one or more compounds selected from the groupformed of alkali-metal halides, alkaline-earth metal halides, andtetra-alkylammonium halides;

The concentration of cellulose formate is at least equal to 18%.

Even more preferably, the composition in accordance with the inventionhas at least one of the following characteristics in the event that itis intended for the manufacture of an industrial fiber:

The composition contains calcium chloride and/or lithium chloride;

The concentration of cellulose formate is at least equal to 20%;

The DP of the cellulose in the cellulose formate is at least equal to600.

The process of the invention is preferably used for the obtaining offibers (spinning process), and it is preferably carried out with anon-coagulating layer of fluid (dry jet wet) which is advantageously alayer of air.

The regenerated cellulose fiber in accordance with the inventionpreferably has at least one of the following properties:

Its degree of substitution by formate groups is less than 2%;

Its elongation upon rupture A_(R) is at least equal to 8%.

The regenerated cellulose fiber in accordance with the inventionpreferably has at least one of the following properties when it is atechnical fiber:

The DP is at least equal to 500;

The tenacity is at least equal to 40 cN/tex;

The initial modulus is at least equal to 1000 cN/tex.

Even more preferably, this industrial fiber has at least one of thefollowing properties:

The DP is at least equal to 600;

The tenacity is at least equal to 50 cN/tex;

The initial modulus is at least equal to 1500 cN/tex.

Of course, the invention is not limited to the embodiments which havebeen indicated above.

Thus, solvents other than those used in the examples can be employed, inparticular N-methylformamide, N-formyl-morpholine, ε-caprolactam,δ-valerolactam, N-methylcaprolactam, N-methylvalerolactam,γ-pyrrolidone, 1,3-dimethyl-2-imidazolidinone,1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone, and tetramethylenesulfoxide, and, as additive, tetra-alkylammonium halides other thanthose indicated in the examples may be used, in particular,tetra-ethylammonium chloride, tetra-butylammonium chloride,tributylmethylammonium chloride, and tricaprylylmethylammonium chloride.

Furthermore, the compositions in accordance with the invention maycontain additives other than those previously mentioned.

The expression "cellulose formate" covers cases in which the alcoholgroups of the cellulose are substituted by groups other than formategroups in addition to the latter, for instance ester groups particularlyacetate groups, the degree of substitution of the cellulose by theseother groups being preferably less than 10%.

We claim:
 1. A composition capable of giving fibers or films having abase of cellulose formate, characterized by the following points:a) thecomposition is a solution; b) the concentration of cellulose formate inthe composition is at least equal to 8% by weight; c) the degree ofsubstitution of the cellulose by formate groups is greater than 20%; d)the composition contains as solvent one or more compounds selected fromthe group consisting of alkylsulfoxides, lactams, acyclic amides andcyclic derivatives of urea.
 2. A composition according to claim 1,characterized by the fact that its content of water and/or of alcohol oralcohols is less than 10% by weight of the solvent or solvents.
 3. Acomposition according to of claim 1, characterized by the fact that thedegree of substitution of the cellulose by formate groups is greaterthan 30%.
 4. A composition according to claim 1, characterized by thefact that the degree of polymerization (DP) of the cellulose in thecellulose formate is equal to at least
 500. 5. A composition accordingto claim 4, characterized by the fact that the DP is at least equal to600.
 6. A composition according to claim 1, characterized by the factthat the concentration of cellulose formate is at least equal to 18%. 7.A composition according to claim 6, characterized by the fact that theconcentration of cellulose formate is at least equal to 20%.
 8. Acomposition capable of giving fibers or films having a base of celluloseformate, wherein:a) the composition is a solution; b) the concentrationof cellulose formate in the composition is at least equal to 8% byweight; c) the degree of substitution of the cellulose by formate groupsis greater than 20%; d) the composition contains as solvent one or morecompounds selected from the group consisting of alkylsulfoxides,lactams, acyclic amides and cyclic derivatives of urea,characterized bythe fact that said composition contains one or more compounds selectedfrom the group consisting of alkali-metal halides, alkaline-earth metalhalides, and tetra-alkylammonium halides.
 9. A composition capable ofgiving fibers or films having a base of cellulose formate, wherein:a)the composition is a solution; b) the concentration of cellulose formatein the composition is at least equal to 8% by weight; c) the degree ofsubstitution of the cellulose by formate groups is greater than 20%; d)the composition contains as solvent one or more compounds selected fromthe group consisting of alkylsulfoxides, lactams, acyclic amides andcyclic derivatives of urea,characterized by the fact that saidcomposition contains one or more compounds selected from the groupconsisting of alkali-metal halides, alkaline-earth metal halides, andtetra-alkylammonium halides, said composition further characterized bythe fact that it contains calcium chloride and/or lithium chloride. 10.A composition capable of giving fibers or films having a base ofcellulose formate, whereina) the composition is a solution; b) theconcentration of cellulose formate in the composition is at least equalto 8% by weight; c) the degree of substitution of the cellulose byformate groups is greater than 20% and said formate groups aresubstantially uniformly distributed throughout the cellulose; d) thecomposition contains as solvent one or more compounds selected from thegroup consisting of alkylsulfoxides, lactams, acyclic amides and cyclicderivatives of urea.
 11. A composition capable of giving fibres or filmshaving a base of cellulose formate, whereina) the composition is asolution; b) the concentration of cellulose formate in the compositionis at least equal to 8% by weight; c) the degree of substitution of thecellulose by formate groups ranges from greater than 20% to 44%; d) thecomposition contains as solvent one or more compounds selected from thegroup consisting of alkyl-sulfoxides, lactams, acyclic amides and cyclicderivatives of urea.
 12. A composition capable of giving fibres or filmshaving a base of cellulose formate, whereina) the composition is asolution; b) the concentration of cellulose formate in the compositionis at least equal to 8% by weight; c) the degree of substitution of thecellulose by formate groups ranges from greater than 20% to about 55%;d) the composition contains as solvent one or more compounds selectedfrom the group consisting of alkyl-sulfoxides, lactams, acyclic amidesand cyclic derivatives of urea.